Pretreatment solution for phosphate coating, method of preparing the same and process of treating metal surfaces



United States Patent PRETREATMENT SOLUTION FOR PHOSPHATE COATING, METHODOF PREPARING THE SAME ggESPROCESS OF TREATING METAL SUR- No Drawing.Application August 2, 1956 Serial No. 601,660

14 Claims. (Cl. 148-615) This invention relates to the art of producingphosphate coatings on metal surfaces, and more particularly to theactivation or pretreatment of metal surfaces for subsequent reactionwith phosphate coating solutions.

It is known, e. g., U. S. Patent 2,310,239 to Jernstedt, that solutionsof disodium phosphate containing titanium activate or prepare a metalsurface for subsequent treatment with phosphate coating solutions sothat the equality of the subsequently applied phosphate coating ,isenhanced and the rate of coating formation is accelerated. The degree ofactivation resulting from treatment with such solutions is notreproducible from batches prepared in identical manner, so thatdifficulties are encountered in commercial applications. Moreover,greater concentrations are required to produce a given degree ofactivation than are actually necessary. I

Accordingly, it is an important object of this invention to provide animproved composition for activating metal surfaces in preparation forreaction with phosphate coating solutions which imparts to the surfacesa given degree of activation at lower concentrations than has heretoforebeen possible.

It is another important object of the invention to provide an improvedmethod for preparing an activating composition whereby to increase thereactivity of the same and to obtain therefrom consistent and reprwducible conditioning effects on metal surfaces.

Still other important objects are to provide an improved process offorming phosphate coatings on metal surfaces and to provide an improvedmethod of pretreating or activating metal surfaces to obtain excellentquality phosphate coatings thereon with greater economies than has beenformerly possible.

In accordance with the invention, it has been discovered in connectionwith titanium-containing pretreatment solutions that the degree ofactivation imparted to metal surfaces for subsequent reaction withphosphate coating solutions is critically related to the manner ofpreparing the pretreatment or activating composition and that thereactivity of the activating composition can be drastically altered bythe method employed in its preparation. Unexpectedly, it has been foundthat if the activating composition is prepared under certain carefullycontrolled conditions, its reactivity or activating ability when inaqueous solution is so greatly invigorated that its properties andeffects are entirely unlike activating compositions heretofore known tothe art. The activating composition resulting from the controlledconditions of preparation as set forth in this invention ischaracterized by its consistent and predictable conditioning action andby its ability to impart a given degree of activation to metal surfacesat considerably lower concentrations than that required of prior artactivating compositions.

In the practice of the invention, metal surfaces are provided withexceptionally fine quality phosphate coatings by subjection to phosphatecoating solutions after having first been activated by preliminarytreatment with "ice an improved activating solution. The activatingsolution is made up from a dried activating composition containing asthe essential ingredients a phosphate of sodium and atitanium-containing compound. The activating composition is preparedunder certain controls which include, among other conditions, lowtemperature initial dispersion of the essential ingredients, though notnecessarily in their final proportions, and a subsequent highertemperature aging treatment. The initial dispersion or intimate mixingof the essential ingredients in theproportions in which they are firstcombined is made to take place for a minimum length of time in anaqueous medium at low temperatures during which the concentration of thehydrogen ion is maintained within certain predetermined limits.Following this critical stage of bringing together initial amounts atleast of the reacting ingredients, the mixture is heated to a minimumtemperature for a minimum length of time during which final amounts maybe added if desired. This stage is hereinafter referred to at times asan aging treatment. A dried activating composition is evolved from theaged mixture, and from this manner of preparation, the reactivity of theactivating composition is so exceptionally enhanced that its ability toactivate metal surfaces is demonstrated when put up in aqueous solutionsin concentrations far below that which was heretofore considerednecessary for proper conditioning. Furthermore, reproducibleconditioning effects and predictable conditioning action, which was theexception with prior art solutions, is consistently obtainable from thesolutions prepared according to the present invention. It has been foundthat such controlled conditions of preparation are critical in order toimpart to the activating composition properties and effects of thecharacter described.

Presently, activating compositions containing titanium are prepared, forexample, by dissolving disodiurn orthophosphate in a small amount of hotwater between and F. and dispersing in the heated solution a solubletitanium compound, e. g., titanyl sulphate. Elevated temperatures areused because of the greater ease of dissolving the solid materials. ThepH of the mixture is adjusted between 8.5 and 9, and the resultingsolution is thereafter dried on a rotary drum drier.

In contrast thereto, in the practice of this invention a solution of atitanium-containing compound is prepared and a phosphate of sodiumeither in solution or the dry salt is dispersed therein. A slurry isformed by the addition of the phosphate compound to the titaniumsolution, which is intimately mixed, preferably for at least tenminutes, at low temperatures, and the pH of the slurry is maintainedbetween a maximum of about 7.8 and a minimum of about 5.7. When the pHof the slurry is outside the range the benefits of the invention are notobtained. Preferably the pH of the slurry is maintained between 6.4 and7.6. Sulphuric acid or sodium hydroxide have been found to be suitablefor adjusting the pH of the slurry when required. The temperature of theslurry during this initial dispersion stage should not exceed a maximumof about 75 F. Lower temperatures are not harmful. Although satisfactoryconditioning has resulted with activating compositions prepared fromslurries that have been held at 50 F. during the initial mixing of theessential ingredients in the proportions in which they are firstcombined, the temperature of the slurry is preferably maintained in therange of about 65 F. to about 70 F.

Commercial titanyl sulphate is the preferred titanium compound to. beused for reasons of economy, but other compounds yielding the titaniumion in solution may be successfully employed, such as titanium potassiumfluoride, as the source of the titaniurnion is not critical. The

titanium compound may be dissolved or dispersed at elevatedtemperatures, but before the addition of the phosphate compound thesolution is cooled to the above mentioned low temperature range forinitial dispersion. It has been found that the titanyl sulphate can bedissolved in dilute acids, e. g., sulphuric acid as well as in Water. Infact, commercially available titanyl sulphate contains a certain amountof sulphuric acid.

The phosphate of sodium that is dispersed in the solution of thetitanium compound in the practice of this invention is disodiumortho-phosphate, and the phosphate of sodium compounds thathave beenfound to be satisfactorily employed in lieu of the disodium phosphateare sodium tripolyphosphate and tetrasodium pyrophosphate or mixturesthereof. The latter two are each especially effective for their ownparticular applications. The quantity of sodium tripolyphosphate and/ ortetrasodium pyrophosphate that may be substituted for the disodiumphosphate is that amount which will produce substantially the sameconcentration of P as the required amount of disodium phosphate.

The above two compounds of sodium may also be used to replace portionsof the required disodiurn phosphate, and in this connection otherphosphates of sodium have been found to be useful in combination withless than the required quantities of disodium phosphate. In some cases,the addition of certain other phosphates of sodium to replace part ofthe required disodium phosphate have produced excellent activatingcompositions comparable in all respects to those resulting from the useof disodium phosphate alone. The other phosphates of sodium that may besuccessfully employed for this purpose are monosodium ortho-phosphateand trisodium ortho-phosphate and mixtures of these. The controllingfactor as to the choice of the particular phosphate of sodium compoundor mixtures of such compounds is the pH of the resulting slurry whencombined with the titanium-containing compound. In general, anycombination of the mentioned phosphate of sodium compounds that yields aslurry having a pH within the critical range above set forth issatisfactory, it being understood that the desired pH is attainedprimarily through the use of the phosphate ion and the sodium ion only,and the introduction of extraneous ions through acids and bases ispreferably avoided.

In preparing the slurry, the amount of titanium-containing compoundemployed is determined from the portions desired in the dried activatingcomposition, and the amount of the phosphate of sodium compound isthereby fixed. Preferably, the amount of titanium-containing compound isselected to produce 1% titanium in the dried powder. However,satisfactory conditioning will result when the concentration of titaniumin the dried powder is as low as 0.005 No practical advantage isrealized in employing more titanium-containing compound in the slurrythan that required to produce 4% titanium in the dried activatingcomposition. The amount of water used in making up the slurry is notcritical and a minimum of water is added since the water must be laterremoved. Warm water may be and usually is employed to dissolve ordisperse the titaniumcontaining compound, and for this purpose waterhaving a temperature of about 170 F. is commonly employed. If thetitanium-containing compound is dissolved or dispersed in warm water,the solution is cooled to the critical range above indicated for theinitial mixing or dispersion of the phosphate of sodium compound. Theamount of the phosphate of sodium compound that is employed is fixed bythe amount of titanium-containing compound desired in the driedactivating -composition. That is to say, the amount of the phosphate ofsodium compound used in making up the slurry is that amount required toproduce a dried activating composition hav ing 0.005% to 4% titaniumbased on the combined 4 weight of the phosphate of sodium compound andthe titanium-containing compound. For example, if commercial titanylsulphate and disodium phosphate are used and it is desired to have aconcentration of 1% titanium in the dried activating compositon based onthe combined weight of titanyl sulphate and disodium phosphate, then forevery 9.7 lbs. of titanyl sulphate added to make up the slurry,approximately lbs. of disodium phosphate should be used.

Although all of the required amount of the phosphate of sodium compoundmay be added to the solution of the titanium-containing compound duringthe initial low temperature dispersion stage, preferably less than therequired amount of the phosphate of sodium compound is added at thistime and the balance is added just prior to or during the highertemperature aging stage. In usual practice, approximately 20% of therequired amount of the phosphate of sodium compound is added during theinitial low temperature mixing of the slurry, although it has been foundthat if as little as 1% of the required amount is added at this time,satisfactory conditioning nevertheless results. When less than therequired amount of the phosphate of sodium compound is added during thelow temperature mixing of the slurry, a particularly advantageous mannerof adding the remainder of the required amount is to add it at anintermediate temperature lower than the temperature to which the slurryis brought for the higher temperature aging treatment. irrespective ofthe amount of phosphate of sodium compound present at this stage, iscontinued for a minimum length of time. The exact minimum time duringwhich the slurry must be maintained under the controlled conditions ofhydrogen ion concentration and temperature previously set forth dependsto some extent upon the quantity of materials handled and is notdefinitely known. Simple tests under operating conditions will determinethe minimum period for a given application. Generally, holding theslurry at these conditions for ten minutes is sufiicient, althoughthirty minutes to one hour is used in practice.

The slurry is then heated to an elevated temperature for the agingtreatment and maintained at this temperature for a minimum length oftime. The pH of the slurry during aging normally does not change fromthat to which it was adjusted for the initial low temperature dispersionstage, and, in any event, is maintained within the limits above setforth for the said dispersion stage. The temperature range in which theaging of the slurry takes place is between about F. and 190 F.Preferably, the aging treatment is carried out between l75 F. and F. Thetime at which the slurry is maintained at the elevated temperatures foraging depends upon the quantities of ingredients handled and even uponthe aging temperature employed. Generally, the slurry must be aged for agreater length of time when lower temperatures are employed. The minimumlength of time cannot be stated with certainty, although generally itcan be said that thirty minutes has been found to be satisfactory.Longer aging periods than this are not harmful, if the temperature ismaintained within the limits indicated. During the aging treatment thepH of the solution is preferably checked to ensure that it is within thestated limits. This can be conveniently done when the remainder of therequired amount of the phosphate of sodium compound is added at theelevated temperature employed for aging of the slurry. The remainder ofthe phosphate of sodium compound, however, as indicated, can be added atlower temperatures, as for example 140 F., while the temperature of theslurry is being raised to the range required for aging. lf thisalternative is employed, the pH of the slurry should be checkedindependently at least once during the aging treatment. As mentioned, ithas been found in practice The low temperature mixing of the slurry,

that no adjustment of the p'His required as the slurry retains the sameacidity as it had during the low temperature mixing treatment.

After the slurry has been aged under the controlled conditions indicatedfor the required length of time, the slurry is dried to form a powderedactivating composition. The manner of drying is notrcritical and, forthis purpose a conventional rotary drum drier canbe employed. Inpractice, the temperature of 'thesurface of the drums in the rotary drumdrier is determined by the temperature of the steam employed, which isusually 80 to 100 lbs. per sq. in. steam.

From the manner of treating the slurry as above described, a driedactivating composition is evolved which contains about 0.005% to 4%titanium based on the combined weight of a soluble titanium-containingcompound and a phosphate of sodium compound. In use, the driedactivating composition is dissolved in water to produce an aqueouspretreatment solution having a concentration of titanium ion between0.0004% and 0.05% and from 0.01% to 2% of the phosphate of sodiumcompound. The pH of the pretreatment solution is generally the same asthe pH of the slurry from which the dried activating composition hasevolved. Metal surfaces contacted with the pretreatment solution,particularly ferrous and zinc metal surfaces, are activated forsubsequent application of coating-phosphate type phosphate coatingsolutions, i. e., conventional zinc, manganese. phosphate coatingsolution. Metal surfaces activated with the pretreatment solutionsprepared as above and subsequently coated with zinc or manganesephosphate coating solutions yield exceptionally fine and densecrystalline coatings at lower concentrations of the pretreatmentsolution than has heretofore been possible. Moreover, the conditioningaction of the pretreatment solution is consistent and results do notvary with different batches prepared following the same technique.

The following are examples of slurries that were prepared for thepurposes indicated in each example, and from each of the slurries, driedactivating compositions containing 1% titanium were evolved by drying atthe same temperature and for the same period of time. Each of the driedactivating compositions .Were put up in aqueous solutions to formpretreatment solutions of dilferent concentration. Unless otherwiseindicated, 20% of the total amount shown for the phosphate of sodiumcompound was added during the low temperature dispersion stage and theremainder was added during the higher temperature aging stage. The lowtemperature dispersion stage was maintained for ten minutes at 70 F. foreach example, and the higher temperature aging treatment was carried outat 180 F. for thirty minutes. The minimum concentration of each driedactivating composition in the pretreatment solution required to producea conditioning or activating effect on mild steel surfaces was noted.The results are given in Table I below.

EXAMPLE 1 A control slurry was prepared as follows:

3.2 gms. commercial titanyl sulphate 30.0 gms. disodium phosphate 60.0ml. water EXAMPLE 2 A slurry was prepared in which the commercialtitanyl sulphate was dispersed in 2.5% aqueous sulphuric acid. The pH ofthe titanyl sulphate was lowered from 0.9

19.2 gms. commercial titanyl sulphate 180.0 gms. disodium phosphate360.0 ml. 2.5% sulphuric acid solution 6 EXAMPLE 3 A slurry was preparedin which sodium tripolyphosphate was employed in lieu of disodiumphosphate;

3.2 gms. commercial titanyl sulphate 16.0 gms. sodium tripolyphosphate60.0 ml. water during the low temperature dispersion stage, 10%, 5%

and 1%, respectively, were added and the remainder of the total amountadded during the higher temperature aging treatment:

EXAMPLE 4 3.2 gms. commercial titanyl sulphate 3.0 gms. disodiumphosphate (initial addition) 27.0 gms. disodium phosphate 60.0 ml. waterEXAMPLE 5 3.2 gms. commercial titanyl sulphate 1.5 gms. disodiumphosphate (initial addition) 28.5 gms. disodium phosphate 60.0 ml. waterEXAMPLE 6 3.2 gms. commercial titanyl sulphate 0.3 gms. disodiumphosphate (initial addition) 29.7 gms. disodium phosphate 60.0 ml. waterEXAMPLE 7 A slurry was prepared employing monosodium phosphate in lieuof disodium phosphate. The resulting pH of the slurry was outside thecritical range.

3.2 gms. commercial titanyl sulphate 29.0 gms. monosodium phosphate 60.0ml. water EXAMPLE 8 A slurry was prepared in which only 5%'of'therequired disodium phosphate was used.

3.2 gms. commercial titanyl sulphate 1.5 gms. disodium phosphate 60.0ml. water The pHof the slurry was not recorded for this example, but itwas obviously outside the critical range as evident from the pH of theresulting pretreatment solution.

The following example illustrates the importance of attaining thedesired pH in the slurry primarily through the use of phosphate ion andsodium ion only, as otherwise such compounds will not be present intheir required amounts.

EXAMPLE 9 To a slurry prepared as in Example 8 was added 1.5 gms. ofsodium carbonate to raise the pH to that of a normal slurry.

EXAMPLE 10 A slurry prepared as in Example 1 was tested for activating'or conditioning ability without proceeding with the step of drying andforming a dried activating composition.

In the following fourexamples, approximately 25% and 50% of the amountof disodium phosphate normally added during the low temperature mixingtreatment was replaced by monosodium and trisodium phosphate, respectively:

7 EXAMPLE 11 19.2 gms. commercial titanyl sulphate 27.0 gms. disodiumphosphate (initial addition) 9.0 gms. monosodium phosphate (initialaddition) 144.0 gms. disodium phosphate 360.0 ml. water EXAMPLE 12 19.2gms. commercial titanyl sulphate 18.0 gms. disodium phosphate (initialaddition) 18.0 gms. monosodium phosphate (initial addition) 144.0 gms.disodium phosphate 360.0 ml. water EXAMPLE 13 19.2 gms. commercialtitanyl sulphate 27.0 gms. disodium phosphate (initial addition) 11.5gms. trisodium phosphate (initial addition) 144.0 gms. disodiumphosphate 360.0 ml. water EXAMPLE 14 19.2 gms. commercial titanylsulphate 18 gms. disodium phosphate (initial addition) 23 gms. trisodiumphosphate (initial addition) 144 gms. disodium phosphate 360 ml. waterIn the following first four examples, approximately 25 50%, 75% and 100%of the amount of disodium phosphate normally added during the highertemperature aging treatment was replaced by monosodium phosphate. In thefifth example, immediately following 25% of the amount of disodiumphosphate normally added during the higher temperature aging treatmentwas replaced by trisodium phosphate. Greater replacements by trisodiumphosphate during this stage acted in identical manner, i. e., resultedin no conditioning ability in the dried activating composition. Disodiumphosphate was added during the low temperature mixing treatment in thenormal manner in all of the five examples immediately following.

EXAMPLE 15 19.2 gms. commercial titanyl sulphate 36 gms. disodiumphosphate 72 gms. monosodium phosphate (final addition) 72 gms. disodiumphosphate (final addition) 360 ml. water EXAMPLE 17 19.2 gms. commercialtitanyl sulphate 36 gms. disodium phosphate 108 gms. monosodiumphosphate (final addition) 36 gms. disodium phosphate (final addition)360 ml. water EXAMPLE 18 19.2 gms. commercial titanyl sulphate 36 gms.disodium phosphate 144 gms. monosodium phosphate (final addition) 360ml. water EXAMPLE 19 19.2 gms. commercial titanyl sulphate 36 gms.disodium phosphate 46 gms. trisodium phosphate (final addition) 108 gms.disodium phosphate (final addition) 360 m1. water Table 1 pH Pre-Minimum concen- Example pH Slurry treatment tration of dried solutionactivated composition, gms./liter 7. 5 7. 5 0.10. 6. 7 6.9 0.32. 7. 350.63. 7. 45 7. 52 0.32. 7. 55 7. 51 0.32. 7. 45 7. 55 0.16. 2. 99 3. 77N o conditioning. 2. 40 Do. 7. 45 7. 60 D0. 7. 5 Do. 7. 2 7.18 0.32. 7.1 7. 18 0.32. 7. 5 7. 35 0.08. 7. 6 7. 75 2.5. 6. 8 7.0 0.32. 6. 4 6. 630.32. 5. 9 6.15 0.63. 5. 0 5. 70 N o conditioning. 8. 0 7. 0 0.

EXAMPLE 20 Batches of dried activating compositions were prepared by thepresent conventional method for comparison with activating compositionsprepared in accordance with the present invention. In accordance withthe present conventional method, for each batch 900 lbs. of disodiumphosphate was dissolved in hot Water at a temperature of 180 F. 97 lbs.of commercial titanyl sulphate, together with a slight amount of causticsoda was added to the solution of disodium phosphate at the elevatedtemperature. The pH of the slurry was maintained at 8.5 and subsequentlydried on a rotary drum to produce a dried activating composition. Thedried activating composition from each batch was dissolved in Water toform pretreatment solutions of difierent concentrations. Out of 277batches tested, 91 batches gave no conditioning at a concentration ofdried activating composition of 5 grams/liter of solution. 124 batchesgave conditioning at 5 grams/liter. 45 batches gave conditioning at 2.5grams/liter. 14 batches gave conditioning at 1.25 grams/liter and 2 gaveconditioning at 0.15 gram/liter.

In contrast, production batches were made in accordance with the presentinvention by dissolving 200 lbs. of disodium phosphate in cold water ata temperature less than 70 F. Separately 97 lbs. of commercial titanylsulphate was dispersed in hot water at 160 F. and cooled down to F.before admixture of this dispersion with the disodium phosphatesolution. The dispersion of titanyl sulphate was mixed with the coldsolution of disodium phosphate at a temperature below F. The pH of theresulting slurry was maintained at 7.3 and the slurry was mixed for 45minutes. Thereafter, the temperature of the mixture was raised to F. andthe remainder of the required amount of disodium phosphate, viz., 700lbs., was added. The mixture was aged for a period of one hour at F. Theslurry was then run onto a rotary drum drier and a dried activatingcomposition was produced. The dried activating composition from eachbatch was dissolved in water. When the above procedure was followed,essentially all of the resulting pretreatment solutions gaveconditioning at a concentration of 0.63 gram of dried activatingcomposition per liter of solution. Substantially all of the batchescould have produced conditioning at even lower concentrations, but thelowest conccntration was not determined for these batches.

What is claimed is:

l. A method of forming a dried activating composition which comprisesthe steps of forming an aqueous slurry consisting essentially of atitanium-containing compound and a phosphate of sodium compound, saidtitanium-containing compound and said phosphate of sodium compound beingpresent in such proportions as to produce a pH of said slurry in therange of about 5.7 to about 7.8, mixing the slurry at a temperaturebelow about 75 F.

and thereafter raising the temperature of the mixed slurry for a periodof time and at a temperature sufficiently elevated to age the slurry sothat a dried activating composition can be evolved therefrom which whendissolved in aqueous solution is capable of activating metal surfacesfor subsequent reaction with phosphate coating solutions, and thereafterdrying the aged slurry to produce a dried activated compositioncontaining at least 0.005 titanium based on the combined weight-of saidtitanium-containing compound and said phosphate of sodium compound insaid dried activating composition.

2. A method of forming a dried activated composition which comprises thesteps of forming an aqueous slurry consisting essentially of atitanium-containing compound and a phosphate of sodium compound, saidtitanium-containing compound and said phosphate of sodium compound beingpresent in such proportions as to produce a pH of said slurry in therange of about 5.7 to about 7.8, said slurry being formed below amaximum temperature of about 75 F., mixing the slurry at saidtemperature and thereafter raising the temperature of the mixed slurrybetween 165 F. and 190 F. to age the slurry, drying the aged slurry toproduce a dried activating composition containing at least 0.005%titanium based on the combined weight of said titanium-containingcompound and phosphate of sodium compound in said dried activatingcomposition.

3. A method of forming a dried activating composition which comprisesthe steps of forming an aqueous slurry consisting essentially of atitanium-containing compound and a phosphate of sodium compound, saidtitanium-containing compound and said phosphate of sodium compound beingpresent in such proportions as to produce a pH of said slurry in therange of about 5.7 to about 7.8, said slurry being formed at atemperature between about 60 F and 75 F., mixing the slurry at saidtemperature and thereafter raising the temperature of the mixed slurrybetween 165 F. and 190 F. to age the slurry, drying the aged slurry toproduce a dried activating composition containing from about 0.005 to 4%titanium based on the combined weight of said titanium-containingcompound and phosphate of sodium compound in said dried activatingcomposition.

4. A dried activating composition capable of activating metallicsurfaces for subsequent reaction with phosphate coating solutionsconsisting essentially of a titanium-containing compound and a phosphateof sodium compound in such proportions to yield from about 0.005% to 4%titanium based on the combined weight of said titaniumcontainingcompound and said phosphate, of sodium compound, said composition beingthe product of claim 3.

5. A pretreatment solution for activating metal surfaces for subsequentreaction with phosphate coating solutions comprising an aqueous solutionconsisting essentially of titanium-containing compound in an amountsuflicient to yield between about 0.0004% to 0.05% titanium ion and from0.01% to 2% of a phosphate of sodium compound, said pretreatmentsolution being the product of dissolving the composition of claim 4 inaqueous medium.

6. In a method of treating a metal surface to produce phosphate coatingsthereon, the step comprising contacting said surface with thepretreatment solution of claim 5.

7. A method of treating metal surfaces to produce phosphate coatingsthereon comprising contacting said surface with the pretreatmentsolution of claim 5 and thereafter contacting said surface with anaqueous acidic solution of a phosphate to form a protective phosphatecoatingthereon.

8. A method of forming a dried activating composi-' tion which comprisesthe steps of forming an aqueous slurry consisting essentially of atitanium-containing compound and a phosphate of sodium compound selectedfrom the group consisting of disodium phosphate, sodiumtripoiyphosphate, and tetrasodium pyrophosphate, saidtitanium-containing compound and said phosphate of sodium compound beingpresent in such proportions as to produce a pH of said slurry in therange of 5.7 to 7.8, said slurry being formed at a temperature below amaximum temperature of about 75 F., mixing the slurry at saidtemperature and maintaining the pH within said range during the mixingstep and thereafter raising the temperature of the mixed slurry between165 F. and 190 F. to age the slurry, drying the aged slurry to produce adried activating composition containing at least 0.005% titanium basedon the combined weight of said titanium-containing compound andphosphate of sodium compound in said dried activating composition.

9. A method according to claim 8 wherein between about 1% and 20% of therequired amount of said phosphate of sodium compound is added during thelow temperature mixing treatment and the remainder of said requiredamount is added during the higher temperature aging treatment.

10. A method according to claim 9 wherein said phosphate of sodiumcompound is disodium phosphate.

11. A method according to claim 8 wherein the phosphate of sodiumcompound is a mixture of disodium phosphate and a phosphate of sodiumselected from the group consisting of monosodium phosphate and trisodiumphosphate.

12. A method of forming a dried activating composition which whendissolved in water is capable of activating metal surfaces forsubsequent reaction with phosphate coating solutions which comprisesmixing a titanium-containing compound and sodium tripolyphosphate in anaqueous medium to form a slurry, drying the slurry to produce a driedactivating composition, the proportion of said titanium-containingcompound and said sodium tripolyphosphate used to form said slurry beingselected to produce at least 0.005% titanium based on the combinedweight of said titanium-containing compound and said sodiumtripolyphosphate in said dried activating composition.

13. A dried activating composition capable of activating metal surfacesfor subsequent reaction with phosphate coating solutions which comprisesa titanium-containing compound and sodium tripolyphosphate in an amountsuflicient to yield at least 0.005% titanium based on the combinedweight of said titanium-containing compound and sodium tripolyphosphate.

14. A pretreatment solution for activating metal surfaces for subsequentreaction with phosphate coatings comprising an aqueous solution oftitanium-containing compound and sodium tripolyphosphate, said solutioncontaining between about 0.0004%-0.05% titanium ion and from about 0.01%to 2% of said sodium tripolyphosphate.

References Cited in the file of this patent UNITED STATES PATENTS2,310,239 Jernstedt Feb. 9, 1943 2,322,349 Jernstedt June 22, 19432,528,787 Roland Nov. 7, 1950 2,743,205 Condon Apr. 24, 1956

1. A METHOD OF FORMING A DRIED ACTIVATING COMPOSITION WHICH COMPRISESTHE STEPS OF FORMING AN AQUEOUS SLURRY CONSISTING ESSENTAILLY OF ATITANIUM-CONTAINING COMPOUND AND APHOSPHATED OF SODIUM COMPOUND, SAIDTITANIUM-CONTAINING COMPOUND AND SAID PHOSPHATEOF SODIUM COMPOUND BEINGPRESENT IN SUCH PROPORTIONS AS TO PRODUCE A PH OF SAID SLURRY IN THERANGE OF ABOUT 5.M TO ABOUT 7.8 MIXING THE SLURRY AT A TEMPERATURE BELOWABOUT 75*F. AND THEREAFTER RAISING THE TEMPERATURE OF THE MIXED SLURRYFOR A PERIOD OF TIME AND AT A TEMPERATURE SUFFICIENTLY ELEVATED TO AGETHE SLURRY SO THAT A DRIED ACTIVATING COMPOSITION CAN BE EVOLVEDTHREEFROM WHICH WHEN DISSOLVED IN AQUEOUS SOLUTION IS CAPABLE OFACTIVATING METAL SURFACES FOR SUBSEQUENT REACTION WITH PHOSPHATE COATINGSOLUTIONS, AND THEREAFTER DRYING THE AGED SLURRY TO PRODUCE A DRIEDACTIVATED COMPOSITION CONTAINING AT LEAST 0.005% TITANIUM BASED ON THECOMBINED WEIGHT OF SAID TITANIUM-CONTAINING COMPOUND AND SAID PHOSPHATEDODIUM COMPOUND IN SAID DRIED ACTIVATING COMPOSITION.